1. Field of the Invention
This invention relates to a control system for use with an adjustable automotive suspension unit, and more particularly to a steering input algorithm for use with such a control system.
2. Disclosure Information
Adjustable automotive suspension units and control systems for use therewith have been the subject of much engineering activity and development. U.S. Pat. No. 4,555,126 discloses and claims a system for adjusting the suspension characteristics of at least the front or rear wheels of a vehicle, such that the oversteer or understeer characteristic of the vehicle is altered. This alteration is done when the steering angle exceeds a predetermined value. Such a system suffers from the inability to anticipate changes in a vehicle attitude resulting from the steering angle. In other words, by the time the adjustable system reacts to a change in steering angle, that change in steering angle may have already caused a change in vehicle attitude and as a result, much of the efficiency of the system is lost. Similarly, French Patent Application No. 2,362,017 discloses a steering responsive system in which an off-center movement of the steering rack triggers a control signal to the system controller. This type of system suffers from yet another deficiency inasmuch as if the system is adjusted to produce a control signal with only minimal displacements of the steering handwheel, one result will be that even unintended motion of the steering handwheel will trigger a control system response. If, on the other hand, this system is adjusted such that a more exaggerated movement of the steering handwheel is required to trigger a controlled response, then it is possible that steering handwheel movements which normally and desirably would demand a controlled response will be unmet by such a response. It is an object of the present invention, then, to provide a steering operation algorithm for use with a control system for adjustable automotive suspension units which quickly provides a control signal in the event that the driver is operating the steering handwheel in a manner which yields a useful and intended input into the vehicle steering system.
Automotive designers have created a variety of control systems in which adjustable suspension units are operated according to the instantaneous position of a steering handwheel. Examples of such systems are disclosed in U.S. Pat. Nos. 4,564,214 and 4,621,833, the latter of which is assigned to the assignee of the present invention.
Other suspension control systems using input from a vehicular steering apparatus have utilized steering handwheel angular velocity as an independent control input variable. U.S. Pat. No. 4,575,116 discloses a system in which different reference values are applied to steering handwheel angular velocity depending on whether the steering handwheel velocity is in a direction away from the steering center or a direction toward the steering center.
European Patent Application No. 0,145,013 discloses a roll-suppressive control system for an automotive suspension system with a variable suspension unit in which the damping capability of the suspension unit is increased in the event that steering angular displacement within a given period exceeds a reference value which varies as a function of vehicle speed. This system suffers from a significant drawback inasmuch as it responds only to the average steering rate value calculated during the variable time period and is therefore unable to respond to instantaneously detected steering rates exceeding a critical value.
European Patent Application No. 0,157,576 discloses yet another steering control algorithm for use with an adjustable suspension unit in which the onset of a turn is used to trigger a firmer suspension setting, whereas the detection of the completion of a turn is used to trigger a return to a normal or softer suspension setting. This system utilizes steering handwheel angular rate as an input to the control algorithm. As such, it may be expected to suffer from the previously described defect residing in any system which utilizes solely steering system angular rate as its primary steering input.
As previously noted, it is an object of the present invention to provide a control system for an automotive suspension unit which will respond to intended input from the vehicle driver by placing adjustable suspension units in a firmer setting only when the driver has moved the steering handwheel purposively but not when the driver moves the handwheel in a manner intended to maintain the vehicle on a continuous heading.
It is an advantage of the present invention that a control system according to this invention will be non-responsive to unwanted or unintentional steering inputs.
It is yet a further advantage of the present invention that a control system according to this invention will provide rapid response to meaningful steering inputs.
Other objects, features and advantages of the present invention will become apparent to the reader.